"I want to be the one to tell my fans, especially the ones trekking to get there," Cyrus posted online.

"I'm so sorry, but some things are out of my control," she said, adding in another message that she was feeling "miserable."

On Tuesday, the 21-year-old cancelled a concert in Kansas City after being hospitalized for a severe allergic reaction to antibiotics. Cyrus was put on "medical rest" on the advice of doctors, according to a statement from her publicist, Meghan Prophet.

She also posted a photo of herself, gowned and posing with a toy, in a hospital bed.

Earlier this month, she cancelled her concert in Charlotte, N.C., citing the flu and doctor-ordered bed rest.

The headline-grabbing, controversial Cyrus is midway through her Bangerz tour of North America and Europe. The former Disney star has drawn criticism as she moves into a more adult music career with her raunchy stage antics and outlandish behaviour.